Wet processing is used extensively during the manufacture of integrated circuits, which typically comprise electronic component precursors such as semiconductor wafers, flat panels, and the like. Generally, the electronic component precursors are placed in a bath or a vessel and then contacted with a series of reactive chemical process fluids and/or rinsing fluids. The process fluids may be used, without limitation, for etching, photoresist stripping, prediffusion cleaning and other cleaning of the electronic component precursors. See, e.g., U.S. Pat. Nos. 4,577,650; 4,740,249; 4,738,272; 4,856,544; 4,633,893; 4,775,532; 4,917,123; and EPO 0 233 184, assigned to a common assignee, and Burkman et al., Wet Chemical Processes-Aqueous Cleaning Processes, pg 111-151 in Handbook of Semiconductor Wafer Cleaning Technology (edited by Werner Kern, Published by Noyes Publication Parkridge, N.J. 1993), the disclosures of which are herein incorporated by reference in their entirety.
For example, electronic component precursors are exposed to reactive chemical process fluids to either dissolve contamination on the electronic component precursors or to etch some part of the surface. After this dissolving or etching is performed, the chemical will adhere to the surface of the electronic component precursors. The adhered chemical must then be rinsed from the surface of the electronic component precursors before treating the electronic component precursors with the next reactive chemical process fluid so that the chemical residue on the precursors does not contaminate the next reactive chemical process fluid. For process control, it is important that the two different process fluids not be mixed together because otherwise the concentration of the second reactive chemical process fluid will be continually diluted by the first reactive chemical process fluid. Additionally, when the chemical treatment steps are carried out in a bath, contamination from one bath could be transferred to the next. Therefore, in current wet processing techniques, a rinse with deionized (DI) water is always performed between each chemical treatment step (i.e., contacting precursors with a reactive chemical process fluid), whether the chemical treatment is done in a bath, full flow vessel, spray chamber, or using other wet bench techniques.
The DI rinse removes the given chemical from the surface of the electronic component precursors after the chemical has performed its function (e.g., cleaning or etching). The DI rinse is also performed to prevent mixing of the reactive chemical process fluids and to prevent one reactive chemical process fluid from contaminating the next reactive chemical process fluid. However, this rinsing step imposes several limitations on the manufacture of electronic components.
It is standard in the industry to rinse the electronic component precursors between chemical treatment steps with DI water until the level of dissolved chemicals is about 10 p.p.b. (i.e., 4-16 Mohm-cm). This requires extensive rinsing. Because DI water tends to be very expensive, rinsing substantially increases the costs of manufacturing electronic component precursors. DI rinsing also takes a long time, sometimes consuming as much as 60% of the total wet processing time, therefore decreasing throughput of the electronic component precursors.
The rinse with DI water can also compromise the integrity of the wet processing techniques. For example, it has been observed that rinsing electronic component precursors with DI water between certain chemical treatment steps causes the formation of undesirable oxide, silica, and/or metal precipitates. Without being bound to any specific mechanism, it is believed that when electronic component precursors are treated with, for example, a first basic process fluid, such as ammonium hydroxide and hydrogen peroxide (SC1), this process fluid etches the silicon surface of, for example, the wafer by growing an oxide on the wafer's surface and then by dissolving the oxide with the ammonia. It is only the hydroxyl (OH-) (or alternatively said, the pH) of the dissociated ammonium hydroxide (NH.sub.4 OH) molecule that dissolves the oxide. The reaction product of SC1 is SiO.sub.3.sup.2-, which is a soluble ion at high pH (and low pH fluoride solutions (i.e., hydrofluoric acid (HF)), an thus, results in a solution of dissolved silica. However, silica precipitates out in the presence of seeds such as iron at neutral pH (i.e., rinse water), and it is not uncommon to have neutral conditions occur during rinsing in any standard wet processing method.
Generally, after the wafers are treated with the first basic process fluid (as discussed above) or any other process fluid, a DI rinse is typically done to remove the chemicals from the surfaces of the wafers. Because the DI rinse tends to decrease the pH of the resultant solution (discussed above), which in turn decreases the solubility of the silica, precipitation of silica generally occurs with rinsing (due to the co-precipitation of silica and metal precipitates in the chemical solution), with the metal ions acting to "seed" this precipitation reaction. The materials thought to be most responsible for the precipitation in the ammonium hydroxide/hydrogen peroxide process fluid are Fe, Al, and Zn. Other precipitate forming metals in this solution are Pb, Cu, Ni, Hg, and Cr. These metals are trace contaminates in chemicals used in electronic component precursor wet processing.
The amount of material needed for precipitate formation is extremely small. For example, for an impurity concentration of 0.1 p.p.b. of Fe in the reaction chamber, there is 1e.sup.-6 g of Fe. At pH 7 and higher, and air saturated water, Fe is found in the form of Fe.sub.2 O.sub.3 or FeOH.sub.3. Consider Fe.sub.2 O.sub.3 (the results are comparable for FeOH.sub.3): the density of Fe.sub.2 O.sub.3 is 5.24 g/cm.sup.3, which after precipitation yields 2.7e.sup.-7 cm.sup.3 in total volume of Fe.sub.2 O.sub.3. If every seed is assumed to be a cube with a side dimension of 0.1 .mu.m. (This is an extremely conservative assumption, since seeds can actually have a much smaller volume). Then there is enough material to make 270,000,000 seeds. Each of these seeds will coagulate the silica (an etch product of SC1) and result in the formation of precipitates. This phenomenon is observed in both wet bench techniques (baths), and in full flow methods. It has been observed that all of these precipitates are formed in the rinsing after treatment with SC1. This is unacceptable for wet chemical processing techniques.
Although the precipitates may be reduced if the DI rinse is done for a long period of time and at elevated temperature, this is not an acceptable solution due to the resulting increased costs and lower output of electronic component precursors.
Thus, there is a need in the art for a simple and efficient method that permits the safe chemical treatment of electronic component precursors, while at the same time eliminating the problems and costs associated with DI rinsing between chemical treatment steps. The present invention addresses these as well as other needs.